A solar cell is a device for converting energy of incident light into electrical energy.
The major types of solar cells are classified into crystalline, amorphous and compound types. Most of the solar cells that are currently distributed in the market are crystalline silicon solar cells. The crystalline silicon solar cells are further classified into monocrystalline type and multicrystalline type. An advantage of monocrystalline silicon solar cells is that improvement of the conversion efficiency is easy because of the high quality of the substrates, while a disadvantage thereof is high production cost of the substrates.
On the other hand, multicrystalline silicon solar cells have a drawback that improvement of the conversion efficiency is difficult due to inferior quality of the substrates, and an advantage that they can be produced at low cost. In addition, with the recent improvement in substrate quality and progress in cell fabrication technology of multicrystalline silicon substrates, a conversion efficiency of about 18% has been achieved at research level.
Meanwhile, since multicrystalline silicon solar cells are mass-produced at low cost, they have conventionally been distributed in the market, and are today's mainstream solar cells.
In recent years, solar cells have been required to have even higher conversion efficiencies. Therefore, various approaches have been devised for the surface electrode (bus bar electrode, finger electrode) arranged on the light receiving surface.
Generally, for example, means such as decreasing optical loss (reflectional loss) by fine wiring, and forming finger electrodes and bus bar electrodes so as to cross orthogonal to each other so that electrons collected in the finger electrodes are carried to bus bar electrodes with minimum loss have been used.
Decreasing the electrode area of the surface electrode thereby to increase the light receiving area is one approach to meet the requirement of further improving the conversion efficiency of solar cells.
However, a problem is that, in particular, when finger electrodes are thinned to decrease the electrode area, the resistance within the electrode increases, resulting in loss.
To solve this problem, increasing the thickness of finger electrode thereby to increase the cross-section area within the electrode and reduce the resistance is considered. However, in reality, there is a limit to the thickness of electrodes when electrodes are formed by screen printing, and the desired thickness can only be obtained through a process including a plural times of printing, and by using expensive equipment, namely, that for sputtering or vapor deposition. This leads to the problem of increase in solar cell production cost.
It is therefore an object of the present invention to provide a solar cell module with a high conversion efficiency and a photovoltaic power generator using this, which is realized by reducing the substantial resistance by increasing the number of bus bar electrodes to reduce the lengths of finger electrodes.
A single solar cell element is seldom used alone, and usually, a plural number of them are connected together to be used as a solar cell module. This is because even the silicon solar cell element that is dominant in the market produces only a low voltage on the order of 600 V when used as a single element and is not practical, the cells therefore need to be series connected to increase the voltage.
While there are various uses of this solar cell module, the most typical use at present is installation of a plural number of solar cell modules on the roofs of general houses. For this use, the solar cell module is required to have a high conversion efficiency for efficient power generation within a limited installation area, and to have excellent design quality and beautiful appearance because the external appearance of a house depends on it.
In order to obtain a solar cell module with high efficiency, apart from using solar cell elements with high efficiency, there have been proposals such as forming irregularities on the glass on the surface of the solar cell module and forming an antireflective film on the surface of the glass so as to effectively introduce light into the solar cell module (refer to Patent Document 1, for example).
Also, a method in which the light diffusion/reflection effect of a protective member on the backside of a solar cell module is enhanced has been proposed (refer to Patent Document 2, for example).
Moreover, enhancing the light diffusion/reflection effect by using white color for a filler member 10 or a back surface protective member 11 is also generally practiced.
In addition, in order to obtain a solar cell module with high design quality, it is effective to form irregularities on the glass on the surface of the module and to form an antireflective film on the surface of the glass as mentioned above (refer to Patent Document 1, for example).
Furthermore, providing an anti-glare film inside the solar cell module so as to prevent reflection on the solar cell module and light pollution and suppress the gloss to a low level has been proposed (refer to Patent Document 3, for example).    [1] Japanese Unexamined Patent Publication No. 2003-124491    [2] Japanese Unexamined Patent Publication No. 2003-234484    [3] Japanese Unexamined Patent Publication No. 2001-203378
FIG. 16 illustrates an end portion of the light receiving surface of a conventional solar cell module, and FIG. 17 illustrates an end portion of the back surface of the same.
FIGS. 18 and 19 are cross-sectional views of the conventional solar cell module.
FIG. 18 is a cross-sectional view taken along the line G-G of FIGS. 16 and 17, and FIG. 19 is a cross-sectional view taken along the line H-H of FIGS. 16 and 17.
In each of the drawings, a solar cell element is denoted by X, a wiring member by 8, a connecting member by 6, a terminal box by 7 and a filler member by 10, respectively.
To connect solar cell elements together, electrodes on the surface are connected to electrodes on the back surface of another solar cell element by the wiring members.
To connect these wiring members 8 to the solar cell, usually, bus bar electrodes are formed in the regions of the solar cell elements where the wiring members 8 pass. In addition, a great number of narrow finger electrodes to be connected to the bus bar electrodes are formed to efficiently collect electric current from the surfaces of the solar cell elements.
A copper foil coated with solder is generally used for the wiring members 8, and they are fused to the bus bar electrodes on the surfaces of the solar cell elements. Since the connecting members 6 are also formed using a solder-coated copper foil as the wiring members 8, as shown in FIG. 16, the wiring members 8 and connecting members 6 with metallic gloss of solder are visible when the solar cell module is viewed from the light receiving surface side.
Meanwhile, the surfaces of the solar cell elements are roughened to improve the efficiency, and an antireflective film is formed to reduce the reflectance so as to effectively introduce the sun light. For this reason, the surfaces of the solar cell elements have a tone of color that is something between blue and dark blue near black.
Moreover, as mentioned above, in order to improve the properties of the solar cell module, the filler member 10 and the back surface protecting member 11 located on the back surface side of the solar cell elements are formed to have white color so as to enhance light diffusion/reflection effect, which is also a generally practiced method.
Accordingly, when the solar cell module is viewed from the light receiving side, the gaps between the solar cell elements have white color in many cases. This difference in color is one factor to deteriorate the design quality of the solar cell module.
In order to solve this problem, there have been proposals including coating the surfaces of the wiring members 8 and connecting members 6 with a colored resin layer (refer to Patent Document 4, for example), and providing a reflected light controlling film over the wiring members 8 to which the solar cell elements are connected (refer to Patent Document 5, for example) so as to make the wiring members 8 and the connecting members 6 less noticeable.
Also proposed is coloring the translucent panel 9 excluding regions that are opposed to the solar cell elements so as to prevent the wiring members 8, connecting members 6 and back surface material among the solar cell elements from being visible (refer to Patent Document 6, for example).
Furthermore, a technique for covering the connecting members 6 with a white sheet so that the connecting members 6 have the same color as that of the back surface material among the solar cell elements has been also devised.    [4] Japanese Unexamined Patent Application No. 2001-339089    [5] Japanese Unexamined Patent Application No. 10-323344    [6] Japanese Unexamined Patent Application No. 7-326789
When irregularities are formed in the glass on the surface of a solar cell module or an antireflective film is formed on the surface of the glass, the sun light is effectively introduced, and light pollution can be prevented. However, in such a case, the following problems arise: the cost for the glass material increases; large scale equipment is necessary for forming an antireflective film on the surface of the glass; and the production cost increases because the number of processes increases. In addition, when irregularities are formed on the surface of the glass, dirt and dust tend to adhere to the solar cell module that is set outside due to exposure to the elements, which intercept the sunlight before it enters the solar cell module, causing the solar cell module to have degraded output characteristics.
Similarly, in the case of a solar cell module provided with an anti-glare film inside thereof, although the problem of light pollution can be prevented, additional materials are required and the production cost increases. In addition, the effect to enhance light diffusion/reflection obtained by using white color for the filler member 10 or a back surface protective member 11 located on the back surface side of the solar cell elements of a solar cell module cannot be expected, which hinders improvement of the properties of the solar cell module.
Using the techniques such as covering the surfaces of the wiring members 8 and connecting members 6 with a colored resin layer, and providing a reflected light controlling film over the wiring members 8 connecting the solar cell elements makes it possible to make the wiring members 8 and connection members 6 less noticeable. However, since covering the surfaces of the wiring members 8 and connecting members 6 causes the problem of increase in material cost and the number of steps, and large scale equipment is required for forming a film on all of the solar cell elements connected through the wiring members 8, the production cost increases.
Using the technique of coloring the translucent panel 9 excluding regions that are opposed to the solar cell elements can prevent the wiring members 8, connecting members 6 and the back surface material seen among the solar cell elements from being visible. However, since this requires an additional step of coloring the translucent panel 9 and positioning between the translucent panel 9 that has predetermined, preliminarily colored regions and the solar cell elements connected through wiring members 8, the process becomes complicated. In addition, the effect to enhance light diffusion/reflection obtained by using white color for the filler member 10 or the back surface material 11 located on the back surface side of the solar cell elements cannot be expected, hindering improvement of the properties of the solar cell module.
As described so far, despite the high market demand, it has been difficult to realize the production of a solar cell module with high efficiency and high design quality at low cost.
The present invention has been made in consideration of the problems above, and an object of the present invention is to provide a solar cell module with high efficiency, high design quality, which is excellent in external appearance and can be produced at low cost.